This invention relates to improvements in the manufacture of fibrous webs, such as paper and the like. More particularly, the invention is directed to improvements in the manufacture of tissue by the air-lay principle.
In the manufacture of fibrous webs such as paper by the air-lay principle, care must be taken to ensure uniformity of distribution of fibers on a forming wire. Air laid fibrous webs have a tendency to undesirable formation of ripples that extend transversely of the forming wire and weaken the web in the machine direction. These ripples form when attempts are made to operate at economical high forming wire velocities in excess of a range from about 500 feet per minute to about 550 feet per minute at economical air velocities in a range of from about 250 to about 300 feet per minute through the forming wire. The ripples do not tend to form at lesser velocities of the forming wire.
U.S. Pat. Nos. 4,004,323, 4,035,870, and 3,748,693 are representative of the prior art, and are believed material to the examination of this application.
U.S. Pat. No. 4,004,323 discloses, in FIG. 2, a formation duct 22A disposed at an angle of incidence B to a linear foraminous forming surface 24A, in a range of from about 10 degrees to about 30 degrees, most preferably about 20 degrees. The patent further discloses that: the front and rear inner surfaces 32A and 34A be divergent at an angle of about 11/2 degrees, but preferably that they be parallel; and that the forming surface speed may be in excess of 200 feet per minute. No criticalities are assigned the velocity of air through the forming surface and the relative velocity of the fibers to the forming surface in the direction of movement of the latter.
U.S. Pat. No. 4,035,870 discloses fiber conduit 10 and forming bell 14 coaxially aligned along an axis disposed at an acute angle to the forming surface 16 of wire 17 so that fibers are deposited on surface 16 in a direction having a vector component coinciding with the direction of movement of surface 16.
U.S. Pat. No. 3,748,693 discloses vanes 54 in a suction box 34 having upstream and downstream air outlets 38. The vanes 54 extend transversely of movement of a forming wire 30 and are selectively adjustable to differentially restrict air flow through wire 30 to vary web thickness.
It is a general objective of this invention to provide an improved apparatus and method for the manufacture of air-laid fiber webs.
It is a further objective of the invention to provide improved apparatus and method for the manufacture of fiber webs wherein the webs are substantially devoid of ripples.
It is a still further objective of the invention to provide improved means for uniformly distributing fibrous material onto a forming wire of apparatus for the manufacture of fibrous webs.